1. Field of the Invention
This invention relates to a position detection device to detect a position indicated by a position indicator, and a position input device comprising this position detection device.
2. Background of the Invention
In the past, position input devices are known which are called pen tablets and comprise a pen-type position indicator and a substantially plate-shaped position detection device. This position input device utilizes the electromagnetic coupling between the position indicator and the position detection device to send and receive weak signals. In recent years, in order to improve the ease of use of position detection devices, there have been demands for more precise and reliable signal transmission and reception between the position indicator and the position detection device. A method has been proposed in which a shield plate is added to the sensor substrate of the position detection device to diminish the effects of noise so that reception accuracy is improved (see for example Japanese Patent Laid-open No. 1-158522).
Recently, expansion of the detectable region (the so-called effective area) of the position input device in which the position of the position indicator can be detected has been sought, in order to improve ease of use; on the other hand, smaller position detection devices are also being sought. In order to respond to these two contradictory demands, the fraction of the housing size occupied by the detectable region has become relatively large. However, as a result of the decrease in the space on the outside of the detectable region, limitations are imposed on design innovations, such as providing larger sensor substrates, or separating circuitry which can be a source of noise from the sensor substrate, and consequently there is the possibility that reception sensitivity may decline. Particularly at the edges of the detectable region, there has been the possibility of a prominent decline in reception sensitivity. As a result, in the past, methods based on software operation have been used to compensate for reduced sensitivity, in anticipation of declines in reception sensitivity.
An object of this invention is, in a position detection device which detects the position indicated by a position indicator, to enable precise and reliable signal reception, while achieving compact size.